Diagnostic criteria for Kleine-Levin syndrome

The following KLS definition was developed by the International Classification of Sleep Disorders - Third Edition (ICSD-3, 2014)

Criteria A to E must be met

A. The patient experiences at least two recurrent episodes of excessive sleepiness and sleep
duration, each persisting for two days to five weeks.

B. Episodes recur usually more than once a year and at least once every 18 months.

C. The patient has normal alertness, cognitive function, behavior, and mood between
episodes.

D. The patient must demonstrate at least one of the following during episodes:

Cognitive dysfunction.

Altered perception.

Eating disorder (anorexia or hyperphagia).

Disinhibited behavior (such as hypersexuality).

E. The hypersomnolence and related symptoms are not better explained by another sleep
disorder, other medical, neurologic, or psychiatric disorder (especially bipolar disorder), or
use of drugs or medications.

These criteria replace the following definition of 2005.

A KLS patient would have symptom A, one or more of the B symptoms, and the pattern described in C.

A. Recurrent episodes of severe hypersomnia (2-31 days)

B. Plus one or more of the associated features:

Cognitive abnormalities such as feeling of unreality, confusion, hallucinations.

Abnormal behavior such as irritability, aggression, odd behavior

Binge eating

Hyper-sexuality

C. Interspersed with long periods of normal sleep, cognition, behavior and mood

While the above definition captures the symptoms experienced by a vast majority of KLS cases, like with any medical condition there are atypical cases or outliers which do not fall within the classic definition. The length of episodes and period of time between episodes in some cases are known to be outside of the periods noted in this definition. The lack of a known medical test to confirm KLS, cause for its onset or its remission means that all of the information available regarding KLS is based on observations of suspected cases. Further, the rarity of illness results in a limited sample size which means that as more data is gathered it is possible that we will find that the definition and typical symptoms will shift.